The properties of synthetically prepared calcium phosphates of biological interest are being studied with a variety of ultrastructural and physical-chamical techniques such as electron microscopy, x-ray diffraction, B-E-T surface area methods, and standard analytical chemistry procedures. Topics under current investigation include (1) the effect of fluoride, magnesium, and carbonate on the formation, growth and physical properties of apatite and of non-apatitic precursor phases such as octacalcium phosphate, and (2) the preparation and characterization of synthetic analogues to intracellular mineral deposits such as occur in mitochondria and in subcellular storage organelles.